Apparatus for implanting an ion on a target and method for the same

ABSTRACT

Anion implantation apparatus includes an ion source for extracting ions therefrom at an extraction voltage, an acceleration pipe for accelerating the ions thus extracted at an acceleration voltage of V A  and a momentum segregation magnet for selecting the ions having a specific momentum from the ions extracted from the acceleration pipe so that the desired ions are caused to be incident on a target. Assuming that M I  denotes the mass number of the desired ions, Z I  denotes the valence thereof, Mc denotes the mass number of noted impurity ions of the impurity ions generated an upstream side of the acceleration pipe, and Z C  denotes the valence thereof, if the relationship that the value of M I ·(V E +V A )/Z I  and that of M C ·V A /Z C  are equal or approximately equal to each other is satisfied, one of the extraction voltage V E  and the acceleration voltage V A  is increased and the other thereof is decreased while the value of (V E +V A ) is maintained substantially constant.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to an apparatus and a method for implantingions on a target, and more particularly relates to the apparatus and themethod for preventing impurity ions, which are different from desiredions in at least one of mass number and energy, from being implanted ona target.

[0003] 2. Description of the Related Art

[0004]FIG. 2 shows an example of an ion implantation apparatus of therelated art. The ion implantation apparatus includes an ion source 2having a plasma production chamber 4 for electrostatically extractingions 8 therefrom, a mass segregation magnet 10 for selectively derivingspecific ions (which are specified by a mass number and valence) fromthe ions 8 extracted from the ion source 2, an acceleration pipe 12 forelectrostatically accelerating the ions 8 derived from the masssegregation magnet 10, and a momentum segregation magnet 14 forselectively deriving the ions having a specific momentum (which isspecified by a mass number and energy) from the ions 8 derived from theacceleration pipe 12. The ion implantation apparatus is constructed sothat only the desired ions derived from the momentum segregation magnet14 are implanted on a target (e.g. substrate such as a semiconductorwafer) 16.

[0005] The target 16 is held on a holder 18 at a ground potential. Ascanner for scanning ions 8 and others not shown are usually providedbetween the momentum segregation magnet 14 and the target 16. A path ofthe ions 8 from the outlet of the ion source 2 to the holder 18 isincluded in a vacuum chamber. The vacuum chamber is not shown.

[0006] The ion source 2 includes the plasma production chamber 4 forgenerating plasma and an extraction electrode 6 for extracting the ions8. The plasma production chamber has a positive potential, and then anextraction voltage V_(E) applied therebetween from a DC extractionelectrode 20. The ions 8 are electrostatically generated from the plasmaproduction chamber 4 by the extraction voltage.

[0007] The acceleration pipe 12 has a plurality of electrodes 13. Theacceleration pipe 12 has a positive potential, and then a voltage V_(A)is applied between an inlet and outlet electrode 13 from a DCaccelerating power source 22. The ions 8 are electrostaticallyaccelerated by the accelerating voltage V_(A) so that the ions 8 hastarget energy.

[0008] Assuming that the valence of the desired ions is Z_(I), the totalenergy E_(T) of the desired ions incident on the target 16 is expressedby the following equation.

E _(T)=(V _(E) +V _(A))×Z _(I) [eV]  [Equation 1]

[0009] Since the following phenomenon occurs between the outlet of themass segregation magnet 10 and the inlet of the acceleration pipe 12,impurity ions which are different from the desired ions may be mixedinto the desired ions in the ion implantation apparatus.

[0010] (1) The energy accelerated by the acceleration pipe 12 is changedby charging conversion in which the desired ions collide with a residualgas. For example, when doubly charged ions are converted into singlycharged ions by the charging conversion, the energy accelerated by theacceleration pipe 12 becomes half of that in the case of the doublycharged ions, if the Voltage V_(A) is constant.

[0011] (2) Where the desired ions are molecular ions, by moleculardissociation, the desired ions change into different ions. For example,when BF₂ ions dissociate into BF ions and F ions, or B ions and F ions,the BF₂ ions no longer are the desired ions.

[0012] (3) A part of the ions 8 collides with the member whichconstitutes an apparatus such as the vacuum chamber so that atoms ormolecules of the member are out of the surface of the member by asputtering to become impurity ions.

[0013] (4) A part of the ions 8 collides with the member whichconstitutes an apparatus such as the vacuum chamber so that atoms ormolecules deposited on or implanted in the member during previousoperation of the ion implantation apparatus are out of the membersurface by sputtering to become impurity ions.

[0014] (5) The gas or vapor used to generating plasma in the plasmaproduction chamber 4 of the ion source 2 flows out from the plasmaproduction chamber 4 into a passage of the ions 8, and then the flowngas or vapor is ionized on the passage to the inlet of the accelerationpipe 12, or otherwise the flown gas or vapor reacts with the atoms ormolecules generated owing to the phenomena of the above items (3) and(4) thereby to become impurity ions.

[0015] In the ion implantation apparatus, it is not preferred that theimpurity ions which are different from the desired ions in at least oneof mass number and energy are implanted into the target 12 together withthe desired ions. Accordingly, a desired implantation characteristic ofthe target cannot be obtained.

[0016] Therefore, when ion implantation with high purity is required asin the example shown in FIG. 2, the momentum segregation magnet 14 asdescribed above as well as the mass number segregation magnet 10 isprovided behind the acceleration pipe 12 in order to derive only theions having a specific momentum selectively.

[0017] The momentum segregation magnet 14 permits the impurity ionsgenerated owing to the phenomena of the above items (1) and (2) to beremoved. The impurity ions having a different momentum from that of thedesired ions are generated in the phenomena of (1) and (2).

[0018] However, in the impurity ions generated by the phenomena of theabove items (3) to (5), the impurity ions which satisfy the followingEquation 2 cannot be separated and removed from the desired ions bymeans of the momentum segregation magnet 14. This applies to the casewhere the left side≈the right side in Equation 2 (that means, the leftside of the Equation 2 is equal or about equal to the right sidethereof). Now it is assumed that M_(T) denotes the mass number of thedesired ions, Z_(I) denotes the valence thereof, M_(C) denotes the massnumber of the impurity ions at issue, and Z_(C) denotes the valencethereof. V_(E) and V_(A) have been already defined.

M _(I)·(V _(E) +V _(A))/Z _(I) =Mc·V _(A) /Z _(C)  [Equation 2]

[0019] Assuming that B is a magnetic flux density, V_(T) is an entireacceleration voltage, m is a mass, and q is a charge, the circlingradius R of the ions in the momentum segregation magnet 14 is expressedby a following Equation 3. Now, assuming that M is the mass number ofthe ions and m_(P) is the mass of a proton, m=M·m_(P). Further, Z is thevalence of the ions and e is an electron weight, q=Z·e. In short,Equation 3 implies that the ions with the same M·V_(T)/Z provides thesame circling radius R.

R=B ⁻¹{square root}{square root over ((2mV _(T) /q))}  [Equation 3]

[0020] Therefore, if the above Equation 2 is satisfied, in the momentumsegregation magnet 14, the circling radii of the desired ions andimpurity ions are equal to each other, both cannot be separated fromeach other. As a result, even with the momentum segregation magnet 14,the impurity ions as well as the desired ions are implanted into thetarget 16. This applies to the case where the left side≅the right sideof the Equation 2 (that means, the left side of the Equation 2 is equalor about equal to the right side thereof).

[0021] A case where the valence Z_(I) of the desired ions and thevalence Z_(C) of the impurity ions at issue are equal to each other(i.e. where Z_(I)=Z_(C)) is typical. For example, both are singlycharged ions. In this case, the above Equation 2 can be represented bythe following equation.

M _(I)·(V _(E) +V _(A))=M _(C) ·V _(I)  [Equation 4]

[0022] If the ion implantation is carried out for the target 16 on thecondition of the Equation 4, the desired ions as well as the impurityions will be implanted into the target 16. This applies to the casewhere the left side≅the right side (that means, the left side of theEquation 2 is equal or about equal to the right side thereof). Suchimplantation is not preferable.

[0023] It can be supposed that the momentum segregation magnet 14 isserved as the mass segregation magnet without providing the masssegregation magnet 10. However, in such a case, the above problembecomes more serious. In case the mass segregation magnet 10 is notpresent, the impurity ions are generated between the outlet (moreparticularly, outlet of the extraction electrode 6) and the inlet of theacceleration pipe 12 in this wider range than the above range.

SUMMARY OF THE INVENTION

[0024] It is an object of the invention to prevent impurity ions, whichare different from desired ions in at least one of mass number andenergy from being implanted into a target together with the desiredions.

[0025] The method for implanting the desired ion on the target accordingto this invention is characterized in that if the relationship ofEquation 2 is satisfied or in Equation 2, the left side≅right side, oneof the extraction voltage V_(E) and the acceleration voltage V_(A) isincreased and the other thereof is decreased while the value of(V_(E)+V_(A)) is substantially constant. The apparatus for implantingthe ion on the target according to the invention is characterized inthat it includes a control device for increasing one of the extractionvoltage V_(E) and the acceleration voltage V_(A) and decreasing theother thereof while maintaining the value of (V_(E)+V_(A)) substantiallyconstant and satisfying the Equation 2.

[0026] When a voltage to be increased or decreased is represented by ΔV,the above Equation 2 after voltage adjustment is converted into thefollowing Equation 5 or Equation 6. Either method of Equation 5 andEquation 6 may be adopted.

M _(I)·{(V _(E) −ΔV)+(V _(A) +ΔV)}/Z _(I) ≠M _(C)·(V _(A) +ΔV)/Z_(C)  [Equation 5]

M_(I)·{(V _(E) −ΔV)+(V _(A) −ΔV)}/Z _(I) ≠M _(C)·(V _(A) −ΔV)/Z_(C)  [Equation 6]

[0027] In both cases of Equation 5 and Equation 6, the value of the leftside and that of the right side are not equal to each other. In thisway, as understood from the explanation of the above Equation 3, in themomentum segregation magnet, since the circling radius of the desiredions and that of the noted impurity ions are made different from eachother, the impurity ions can be removed by the momentum segregationmagnet to derive selectively only the desired ions which are implantedinto the target. Namely, it is possible to prevent impurity ions whichare different from the desired ions in at least one of their mass numberand energy from being implant*ed into the target together with thedesired ions.

[0028] Further, when the above voltage is adjusted, since the value of(V_(E)+V_(A)) which is a sum of the extraction voltage V_(E) and theacceleration voltage V_(A) is kept substantially constant, it is notnecessary to vary the total energy of the desired ions on the target.For this reason, the initial ion implanting condition of the desiredions can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a schematic view showing an exemplary ion implantationapparatus for implementing the running method according to thisinvention; and

[0030]FIG. 2 is a schematic view of an exemplary conventional ionimplantation apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031]FIG. 1 is a schematic view showing an exemplary ion implantationapparatus for implementing a running method according to this invention.Referring to FIG. 1, with like reference numerals referring to likeparts in FIG. 2 showing a prior art, different points of this inventionfrom the prior art will be mainly explained below.

[0032] In the ion implantation apparatus, a magnitude of the outputvoltage produced form each of an extraction power source 20 and anacceleration power source 22 is variable. In the ion implantation, acontrol device 24 controls the extraction power source 20 and theacceleration power source 22 to increase or decrease the extractionvoltage V_(E) outputted from the extraction power source 20 and theacceleration voltage V_(A) outputted from the acceleration power source22.

[0033] In this ion implantation apparatus, an explanation will be givenof a case where after As ions have been implanted into a target 16 for along time, desired BF₂ ions in place of the As ions are implanted.

[0034] Since As ions has been implanted into the target 16 for a longtime, a large amount of As atoms or As molecules has been deposited onor implanted in the member such as a vacuum chamber which constitutesthe ion implantation apparatus.

[0035] In case where desired BF₂ ions (mass number of 49) with totalenergy of 115 keV are implanted on the above-condition. The extractionvoltage V_(E) is 40 kV. The acceleration voltage V_(A) is 75 kV. As theimpurity ions, the As ions (mass number of 75) sputtered owing to theBF₂ ions are noted. It is assumed that the valence of BF₂ ions and Asions is 1.

[0036] In this case, the left side and right side of above Equation 2(or Equation 4) are represented by the following Equation 7 and Equation8.

The left side=M _(I)·(V _(E) +V _(A))=49×(40+75)=5635  [Equation 7]

The right side=M _(C) ·V _(A)=75×75=5625  [Equation 8]

[0037] Therefore, if any means is not taken, in Equation 2 (or Equation4), the left side≈the right side. The difference between both sides isas very small as about 0.2%. Owing to this, the momentum segregationmagnet 14 cannot separate the As ions with 75 keV from the BF₂ ions with115 keV so that the As ions will be implanted into the target 16together with the desired BF₂ ions with 115 keV.

[0038] In order to avoid the above situation, the above voltageadjustment will be implemented. For example, the voltage ΔV is set for10 kV, and the extraction voltage V_(E) is decreased by 10 kV to be setfor 30 kV. The acceleration voltage V_(A) is increased by 10 kV to beset for 85 kV. This increasing or decreasing method corresponds to theexample of Equation 5 described above. Thus, the left side and rightside of the above Equation 2 (or Equation 4) can be represented as thefollowing Equation 9 and Equation 10, respectively.

The left side=M _(I)·(V _(E) +V _(A))=49×(30+85)=5635  [Equation 9]

The right side=M _(C) ·V _(A)=75×85=6375  [Equation 10]

[0039] As a result, in Equation 2 (or Equation 4), the left side theright side. The difference in the value between both sides is about 12%.Therefore, the momentum segregation magnet 14 can sufficiently separatethe As ions with 85 keV from the desired BF₂ ions with 115 keV. Thus,only the desired BF₂ ions can be selectively implanted into the target16. Additionally, the total energy of the desired BF₂ ions remains 115ekV.

[0040] The lower limit of the difference to be given between the leftside value and the right side value in Equation 2 (or Equation 4)depends on a resolution of the momentum segregation magnet 14.Therefore, the limit of the difference may be larger than the resolutionof the momentum segregation magnet 14. For example, the lower limit ispreferably 5% or so. The upper limit is not particularly given. As thedifference increases, the separation by the momentum segregation can beeasily implemented more easily. However, since the difference is notrequired to be excessively, actually, for example, the upper limit maybe 50%.

[0041] In contrast to the above case, as mentioned above, the extractionelectrode V_(E) may be increased by ΔV and the acceleration voltageV_(A) may be decreased by ΔV. This increasing or decreasing methodcorresponds to the example of the above Equation 6.

[0042] In this embodiment, the voltage adjustment of increasing ordecreasing the extraction voltage V_(E) and the acceleration voltageV_(A) as described above can be carried out through the control by thecontrol device 24. However, the voltage adjustment may be carried out bythe other means such as manual setting without using the control device24.

[0043] Further, also in the case where the mass segregation magnet 10 isnot provided and the momentum segregation magnet 14 is served as themass segregation magnet, as described above, the method according thisinvention can be applied to the case. In this case, the impurity ionsgenerated between the outlet of the ion source 2 and the inlet of theacceleration pipe 12 are noted.

[0044] As described hitherto, in accordance with this invention, in themomentum segregation magnet, since the circling radius of the desiredions and that of the noted impurity ions are made different from eachother, the impurity ions can be removed by the momentum segregationmagnet to derive selectively only the desired ions which are implantedinto the target. Namely, it is possible to prevent impurity ions whichare different from the desired ions in at least one of their-mass numberand energy from being implanted into the target as well as the desiredions. Further, even when the above voltage adjustment is implemented,since the value of (V_(E)+V_(A)) which is a sum of the extractionvoltage V_(E) and the acceleration voltage V_(A) is kept substantiallyconstant, it is not necessary to vary the total energy of the desiredions incident on the target. For this reason, the initial ion implantingcondition by the desired ions can be maintained.

What is claimed is:
 1. An apparatus for implanting an ion on a target,the apparatus comprising: anion source for electrostatic ally extractingions from the ion source at an extraction voltage of V_(E); anacceleration deice for electrostatically extracting the extracted ion atan acceleration voltage of V_(A); a momentum segregation magnet forselectively deriving desired ions having a specific momentum from theextracted ions so that the desired ions derived from the momentumsegregation magnet are implanted on the target; and a control deviceincreasing one of the extraction voltage V_(E) and the accelerationvoltage V_(A) and decreasing the other of the extraction voltage V_(E)and the acceleration voltage V_(A) while keeping the value of(V_(E)+V_(A)) substantially constant and satisfying a following equationA as follows: M _(I)·(V _(E) +V _(A))/Z _(I) M _(C) ·V _(A) /Z _(C) 2.The ion implantation apparatus according to claim 1, wherein the controldevice increases one of the extraction voltage V_(E) and theacceleration voltage V_(A) by ΔV and decreases the other of theextraction voltage V_(E) and the acceleration voltage V_(A) by ΔV whilesatisfying a following equation B as follows: M _(I)·{(V _(E) −ΔV)+(V_(A) +ΔV)}/Z _(I) ≠M _(C)·(V _(A) +ΔV)/Z _(C)
 3. The ion implantationapparatus according to claim 1, wherein the control device increases oneof the extraction voltage V_(E) and the acceleration voltage V_(A) by ΔVand decreases the other of the extraction voltage V_(E) and theacceleration voltage V_(A) by ΔV while satisfying a following equation Cas follows: M _(I)·{(V _(E) +ΔV)+(V _(A) −ΔV)}/Z _(I) ≠M _(C)·(V _(A)−ΔV)/Z _(C)
 4. A method for implanting an ion on a target, comprisingthe steps of; a) extracting ions electrostatically at an extractionvoltage of V_(E); b) extracting the extracted ion electrostatically atan acceleration voltage of V_(A); c) deriving desired ions having aspecific momentum from the extracted ions so that the desired ions areimplanted on the target; d) increasing one of the extraction voltageV_(E) and the acceleration voltage V_(A) and decreasing the other of theextraction voltage V_(E) and the acceleration voltage V_(A) whilekeeping the value of (V_(E)+V_(A)) substantially constant and satisfyinga following equation A as follows: M _(I)·(V _(E) +V _(A))/Z _(I) =Mc·V_(A) /Z _(C)
 5. The method according to claim 4, wherein the controldevice increases one of the extraction voltage V_(E) and theacceleration voltage V_(A) by ΔV and decreases the other of theextraction voltage V_(E) and the acceleration voltage V_(A) by ΔV whilesatisfying a following equation B as follows: M _(I)·{(V _(E) −ΔV)+(V_(A) +ΔV)}/Z _(I) ≠M _(C)·(V _(A) +ΔV)/Z _(C)
 6. The method according toclaim 4, wherein the control device increases one of the extractionvoltage V_(E) and the acceleration voltage V_(A) by ΔV and decreases theother of the extraction voltage V_(E) and the acceleration voltage V_(A)by ΔV while satisfying a following equation C as follows: M _(I)·{(V_(E) +ΔV)+(V _(A) −ΔV)}/Z _(I) ≠M _(C)·(V _(A) −ΔV)/Z _(C)